1. Field of the Invention
This invention relates to the control of fluid to a nozzle and, more particularly, to a fluid pressure regulator having a duty cycle controlled, solenoid valve for controlling fluid to a nozzle which is subject to varying downstream pressure and a pressure dependent feedback means for modifying the fluid pressure to account for variation in downstream pressure.
2. Description of the Relevant Art
Advancement in emission technologies for internal combustion engines has resulted in significantly lowered total engine emissions. In general, automotive emission applications employ an exhaust mounted catalytic treatment device for the reduction of regulated exhaust constituents such as Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NO.sub.x) in the engine exhaust prior to its release to the atmosphere. The catalyst treatment devices, or catalytic converters, rely on the latent heat of the exhaust gas to become catalytically active following a cold start. Initiation of catalyst activity occurs at the light-off temperature and is typically in the area of 400 degrees C. A vehicle may require 75-100 seconds or more before the engine exhaust supplies enough heat to reach catalyst light-off. The need to preheat a catalytic converter prior to efficient emission conversion suggests that significant vehicle tailpipe emissions of regulated constituents occur prior to converter light-off. Accordingly, to reduce cold-start emissions, it is desirable to provide an additional heat source to the exhaust stream at engine start-up, thereby promoting faster heating of the converter and a shorter time to optimal catalyst efficiency.
One method of preheating catalytic converters involves the use of fueled burner systems which combust gaseous or liquid fuel in an exhaust mounted burner for a short time following engine start-up. Such systems generally require a combustor mounted in a burner housing having an outlet in communication with engine exhaust gas. The burner requires a fuel supply and means such as a fuel injector or nozzle for introducing the fuel to the combustor. In addition, combustion air must be supplied and mixed with the fuel in a proportion which results in optimum fuel/air mixture for combustion. An ignition source, such as a spark plug, ignites the fuel/air mixture in the combustor.
The burner fuel supply is most conveniently an extension of the engine fuel supply and, consequently, should be configured so as not to compromise the operation of that system, or be affected by it. Substantially instantaneous ignition and reliable operation of the burner is a requirement and, as such, the fuel supply must be able to compensate rapidly to changes in pressure differential across the fuel discharge nozzle caused by exhaust backpressure variation and to changes in fuel supply pressure caused by changes in engine operation. It is desirable to render such backpressure and fuel pressure variations transparent to the burner allowing fueling to occur in a manner consistent with the goals of the burner control strategy.
Accordingly, an object of the present invention is to provide a fuel pressure regulator, for use with an exhaust gas burner, capable of supplying fuel to a fuel nozzle in such a manner as to maintain a desired pressure differential across the nozzle regardless of exhaust backpressure variation on the downstream, or outlet side of the nozzle, and regardless of fuel supply pressure. Response to system changes must occur rapidly to permit fast and reliable ignition and operation of the burner.
Another object of the present invention is to provide a solenoid actuated fuel pressure regulator capable of continuously modulating pressure differential relative to a predetermined input percent duty cycle.
Another object of the present invention is to provide an electric pressure regulator having a minimum internal volume with no fuel recirculation, which can be reverse-purged following burner operation to prevent discharge of unburned fuel to the burner.